Optimal sleep is essential for child growth, development, and immune function. Few studies have evaluated factors associated with sleep duration in childhood from a longitudinal perspective.This study aimed to identify trajectories of sleep duration in childhood and associated maternal and child characteristics.Sleep duration was assessed by maternal report at 3, 12, 24, and 48 months among children from the Pelotas (Brazil) 2004 Birth Cohort. Independent variables included family income, maternal and child demographics, and clinical characteristics. Trajectory analysis was carried out using a semi-parametric, group-based modelling approach. Multinomial logistic regression provided odds ratios (ORs) and 95% confidence intervals (CIs) for the associations between independent variables and sleep duration trajectory groups.A total of 3824 participants were included in the analyses. Three trajectories of sleep duration were identified: "short sleepers" (9.1%), "typical sleepers" (72.1%), and "initially longer sleepers" (18.8%). When compared to typical sleepers, children from less schooled mothers (OR 1.82, 95% CI 1.26, 2.62) and those whose mothers reported depressive symptoms during pregnancy (OR 1.31, 95% CI 1.02, 1.68) and consumed alcohol beverages at 3 months post-partum (OR 1.60, 95% CI 1.03, 2.50) were more likely to be short sleepers. Children who shared the bedroom with another child were about 40% (OR 1.41, 95% CI 1.07, 1.87) more likely to be short sleepers. None of the investigated maternal and child characteristics remained associated with the "initially longer sleeper" group.Among the identified trajectories, the group with short sleep duration trajectory deserves special attention given the importance of adequate sleep duration in the first years of life for the child's growth and development and the high concomitance of other risk factors, such as less schooled mothers, and mothers who reported depressive symptoms during pregnancy and consumed alcohol at 3 months post-partum.